1. Field of the Invention
The present invention relates to a calibration method and related device for a power amplifier, and more particularly, to a calibration method and related device for enhancing output linearity of the power amplifier according to characteristic parameters of the power amplifier.
2. Description of the Prior Art
A power amplifier is the most important component in radio frequency circuitry of a wireless communications system. A power amplifier with large output power usually exhibits output power saturation and low output linearity, which results in decreased output signal quality. It is therefore an important issue to avoid output signal distortion and enhance output linearity of the power amplifier.
A predistortion method, which performs digital signal processing on baseband signals through a predistorter, compensates for signal distortion resulting from nonlinear characteristics of the power amplifier for enhancing output linearity. Please refer to FIG. 1, which is a calibration circuit 10 according to the prior art. The calibration circuit 10 implements the conventional predistortion method. The calibration circuit 10 comprises a predistorter 100, a D/A converter 102, a power amplifier 104, an analog processing unit 106, an A/D converter 108 and a signal generator 110, which form a closed loop to perform the predistortion method for enhancing output linearity of the power amplifier 104. The predistorter 100 performs a signal compensation process on a digital input signal to compensate for signal distortion of the power amplifier 104 in advance. The D/A converter 102 converts the input signal to an analog output signal, and the power amplifier 104 amplifies the output signal.
At the same time, the analog processing unit 106 coupled to the output terminal of the power amplifier 104 performs a signal process on the output signal outputted by the power amplifier 104, and the A/D converter 108 converts the output signal to a digital signal. The signal generator 110 receives the digital signal and generates a calibration signal, which is sent to the predistorter 100, according to the digital signal. Therefore, the predistorter 100 performs the signal compensation process on a next digital input signal according to the calibration signal.
From the above, the calibration circuit 10 generates the calibration signal via a complicated circuit including the analog processing unit 106, the A/D converter 108 and the signal generator 110. Using the calibration circuit 10 to enhance output linearity of a power amplifier is also expensive.